The 6 expertise gained from the Protection talent defiance persists after respec until you change stance.
Theoretically this means you could respec to fury or arms while in zerker stance from prot and then not change stance for the entirety of a boss fight and (unless this is a purely visual bug) benefit from the +6 expertise. I zoned into stocks to see if it changes on UI refresh but neither that nor /reload or a full logout/back in causes the expertise to go away
The 6 expertise gained from the Protection talent defiance persists after respec until you change stance.
Theoretically this means you could respec to fury or arms while in zerker stance from prot and then not change stance for the entirety of a boss fight and (unless this is a purely visual bug) benefit from the +6 expertise. I zoned into stocks to see if it changes on UI refresh but neither that nor /reload or a full logout/back in causes the expertise to go away
video
as you can see, when you spec into defiance you don't gain the 6 expertise either right away, the whole thing is triggered on stance change.